DNA: The Genetic Material

1. Molecular Genetics Section 1 DNA: The Genetic Material Griffith • Performed the first major experiment that led to the discovery of DNA as the genetic material

2. Molecular Genetics Section 1 DNA: The Genetic Material Avery • Identified the molecule that transformed the R strain of bacteria into the S strain • Concluded that when the S cells were killed, DNA was released • R bacteria incorporated this DNA into their cells and changed into S cells.

3. Molecular Genetics Section 1 DNA: The Genetic Material Hershey and Chase • Used radioactive labeling to trace the DNA and protein • Concluded that the viral DNA was injected into the cell and provided the genetic information needed to produce new viruses

4. Molecular Genetics Section 1 DNA: The Genetic Material DNA Structure • Nucleotides • Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base

5. Molecular Genetics Section 1 DNA: The Genetic Material Chargaff rule: for every adenine there is a thymine. For every guanine there is a cytosine, • Chargaff’s rule: C = G and T = A

6. One team

7. Molecular Genetics Section 1 DNA: The Genetic Material X-ray Diffraction • X-ray diffraction data helped solve the structure of DNA • Indicated that DNA was a double helix

8. James Watson (Left) and Francis Crick (right)

9. Molecular Genetics Section 1 DNA: The Genetic Material Watson and Crick • Built a model of the double helix that conformed to the others’ research two outside strands consist of alternating deoxyribose and phosphate cytosine and guanine bases pair to each other by three hydrogen bonds thymine and adenine bases pair to each other by two hydrogen bonds

10. Molecular Genetics Section 1 DNA: The Genetic Material DNA Structure • DNA often is compared to a twisted ladder. • Rails of the ladder are represented by the alternating deoxyribose and phosphate. • The pairs of bases (cytosine–guanine or thymine–adenine) form the steps.

11. Molecular Genetics Section 1 DNA: The Genetic Material Orientation • On the top rail, the strand is said to be oriented 5′ to 3′. • The strand on the bottom runs in the opposite direction and is oriented 3′ to 5′.

12. Molecular Genetics Section 1 DNA: The Genetic Material Chromosome Structure • DNA coils around histones to form nucleosomes, which coil to form chromatin fibers. • The chromatin fibers supercoil to form chromosomes that are visible in the metaphase stage of mitosis.

13. Parental strands of DNA separate. They serve as templates, and produce DNA molecules that have one strand of parental DNA and one strand of new DNA. Molecular Genetics Let’s draw Section 2 Replication of DNA Semiconservative Replication

14. Molecular Genetics Section 2 Replication of DNA Steps. Of DNA Replication 1. DNA helicase, an enzyme, is responsible for unwinding and unzipping the double helix. 2. DNA polymerase, another enzyme, adds appropriate nucleotides using the original DNA as a templete. 3. The leading strand is build continuously, the lagging strand is build discontinuously in Okazaki fragments. 4. DNA ligase, another enzyme, closes up any gaps in the new DNA strand.

15. Molecular Genetics Section 2 Replication of DNA Comparing DNA Replication in Eukaryotes and Prokaryotes • Eukaryotic DNA unwinds in multiple areas as DNA is replicated. • In prokaryotes, the circular DNA strand is opened at one origin of replication.

16. Molecular Genetics Section 3 DNA, RNA, and Protein • RNA • Contains the sugar ribose and the base uracil instead of thymine • A-U G-C • Usually is single stranded

17. Molecular Genetics Section 3 DNA, RNA, and Protein Messenger RNA (mRNA) • Long strands of RNA nucleotides that are formed complementary to one strand of DNA Ribosomal RNA (rRNA) • Associates with proteins to form ribosomes in the cytoplasm Transfer RNA (tRNA) • Smaller segments of RNA nucleotides that transport amino acids to the ribosome

18. Molecular Genetics • DNA is unzipped in the nucleus and RNA polymerasebinds to a specific section where an mRNA will be synthesized. Section 3 DNA, RNA, and Protein Transcription • Through transcription, the DNA code is transferred to mRNA in the nucleus.

19. Molecular Genetics Section 3 DNA, RNA, and Protein RNA Processing • The code on the DNA is interrupted periodically by sequences that are not in the final mRNA. • Intervening sequences are called introns. • Remaining pieces of DNA that serve as the coding sequences are called exons. DNA and Genes

20. Molecular Genetics Section 3 DNA, RNA, and Protein The Code • Experiments during the 1960s demonstrated that the DNA code was a three-base code. • The three-base code in DNA or mRNA is called a codon.

21. Molecular Genetics Section 3 DNA, RNA, and Protein Translation • In translation, tRNA molecules act as the interpreters of the mRNA codon sequence. • At the middle of the folded strand, there is a three-base coding sequence called the anticodon. • Each anticodon is complementary to a codon on the mRNA.

23. Molecular Genetics Section 3 DNA, RNA, and Protein

24. Molecular Genetics Section 4 Gene Regulation and Mutation Mutations • A permanent change that occurs in a cell’s DNA is called a mutation. • Types of mutations • Point mutation • Insertion • Deletion

25. Molecular Genetics Section 4 Gene Regulation and Mutation

26. Molecular Genetics Section 4 Gene Regulation and Mutation Protein Folding and Stability • Substitutions also can lead to genetic disorders. • Can change both the folding and stability of the protein

27. Molecular Genetics Section 4 Gene Regulation and Mutation Causes of Mutation • Can occur spontaneously • Chemicals and radiation also can damage DNA. • High-energy forms of radiation, such as X rays and gamma rays, are highly mutagenic.

28. Molecular Genetics Section 4 Gene Regulation and Mutation Body-cell v. Sex-cell Mutation • Somatic cell mutations are not passed on to the next generation. • Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.